Action films are a lot like pizza: cheesy, nutrition-free, covered in red sauce and delicious nonetheless. The greats, such as “Die Hard” and “Terminator 2,” are gourmet pies, made with the best ingredients possible and cooked to perfection. Then there are the Papa John’s and Pizza Huts of action cinema, entertaining but disposable works such as last year’s underappreciated “White House Down.” But the truly forgettable pizza and action flicks have the most in common — stale, greasy slices of lukewarm mediocrity. “Jack Ryan: Shadow Recruit,” unfortunately, falls into that undesirable category, and its tepid story and nonsensical action sequences render it the rough equivalent of a burned slice of Little Caesar’s.

“Jack Ryan: Shadow Recruit” casts Chris Pine as the famed Tom-Clancy character, telling the story of Ryan’s origin via a tragic helicopter accident that puts him in league with gorgeous physical therapist Cathy Muller (Keira Knightley) and CIA recruiter Thomas Harper (Kevin Costner). Ten years later, Ryan is an undercover analyst working for banks to uncover terrorist funding when he stumbles upon a plot by Russian banker Viktor Cherevin (Kenneth Branagh) to tank the U.S. economy.

The biggest shortcoming of “Jack Ryan” is Adam Cozad’s and David Koepp’s script, which was retrofitted from an original screenplay by Cozad and robbed of any personality in the process. Several individual moments in “Jack Ryan” work, such as Muller’s suspicions about her boyfriend’s job or the brawl between Ryan and a thwarted assassin sent by Cherevin, but only when removed from the context of the film as a whole. Just after Ryan dispatches the aforementioned assassin, his next move is to visit Cherevin, putting on a happy face like they’ve both forgotten the banker tried to have him killed a few scenes ago. The movie is clumsily tied together by a barrage of convenient expository bursts late in the film, but the plot doesn’t even have a handle on its own time line. An early scene informs us that Ryan has been on the job for a full decade — despite not aging a day — yet Muller and Ryan repeatedly state they’ve known each other for only three years.

If the cast were a bit stronger, these logical inconsistencies would be easier to overlook. The reliably charismatic Pine is dead in the water here — the charming, funny personality he brought to his role in “Star Trek” replaced with dutiful, unambiguous heroism. Knightly seems to have been cast solely so Branagh could get as many unflattering reaction shots as possible, but, even when she’s allowed to act, the only thing more unconvincing than her performance is her ludicrous character arc. Meanwhile, Branagh generically glowers as the film’s villain, and Costner ably plays Ryan’s loyal mentor.

But even the lousiest action films should shine when it’s time for their hero to brawl. For one sequence in which Ryan breaks into Cherevin’s office while Muller improbably distracts the villain with whispered flirtations, “Jack Ryan” comes alive, and there’s a glimpse of a taut, exciting espionage thriller. The rest of the film’s action scenes range from adequate to incompetent, especially in the finale, which cuts between several action beats with a stunning disregard for geography, coherence and logic before ending on a moment that makes no sense on its own and even less when tied to the rest of the sequence.